Regina,

One way to differentiate between via holes and component holes is by
design.

Component holes need to be sized correctly for the lead or pin that
will be soldered into it.  Component holes also need special attention
to the amount of copper conductor area coming from the hole to the
surrounding power, ground or circuit layers for proper solderability
(i.e., thermal relief).  Too much copper coming from the hole will not
allow the solder in the hole to reach its melting point when heat is
applied.  Copper is a very good conductor of heat.

Via holes only need to be sized for reliability.  The thinner the
board (or thickness of dielectric for micro-via surface laminar boards
or buried vias) and the lower the normal direction coefficient of
thermal expansion (CTE), the smaller the via holes can be.

Stated simply, via holes can be much smaller than component holes.
Their design function dictates their size.
--
Karl Sweitzer                     voice: 716.47.77546
Eastman Kodak Company             pager: 716.25.33681
800 Lee Road                        fax: 716.47.77293
Rochester, NY 14650-3118         mailto:[log in to unmask]

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